It is often desirable to reconstruct images of structures existing within an imaged object from a set of projection radiographs. In medical applications, anatomical structures such as organs, blood vessels and bones may be imaged.
Prior systems for providing such images have commonly utilized computed tomography (CT) technology. In CT, both an x-ray source and an x-ray detector move on a circular path around a common axis, and a very high number of projection radiographs (or images) are acquired.
In contrast, in tomosynthesis processes, relatively few radiographs are acquired for varying x-ray source positions. Typically the x-ray source assumes positions that are essentially on one side of the object, while the detector (or film) assumes positions on the opposite side of the object.
Digital tomosynthesis (DT) is a method of reconstructing cross sections of a 3D body from its 2D radiographic projections, which is a much faster method than the CT approach for obtaining cross sections. In CT, projections must be acquired from at least 180 degrees plus the fan angle around the object to produce an exact reconstruction of the object. DT, however, exploits projections from limited angles to reconstruct cross sections of the object.
Although the reconstruction is less precise and the plane of reconstruction is limited to one orientation only, DT has the benefit of using a smaller number of projections. This translates into faster data acquisition and provides the advantage of being able to reconstruct objects where space and size limitations prevent one from acquiring projections from all angles. In some clinical situations, exact reconstruction is not necessary, making a fast DT ideal.
Generally, DT image acquisition, reconstruction and readout are carried out by a processing unit such that the time required for such processes is limited. Imaging time depends on detecting a quantum of photons and is therefore a function of both the efficiency of the image screens as well as the allowable signal-to-noise ratio. Conventional image detection screens can produce images with a rate of 15-30 images per second. The time required to acquire an image is generally a function of several factors including the readout time for the image detector, required duration of exposure to generate an image and the heat dissipation capabilities of the x-ray source. The time required for the image acquisition can be reduced by using more efficient imaging screens so as to increase the imaging capacities thereby reducing the amount of radiation required and limiting exposure times. Similarly, DT reconstruction may be accelerated by special purpose hardware making its contribution to the overall process timing negligible.
The image processing and reconstruction time may be reduced by increasing the compute power. The image processing and reconstruction time could be made to be relatively minor compared to the total time. The imaging time will be primarily a function of the mechanical movement required to position the x-ray source relative to the object to be imaged.
Therefore, it would be desirable to provide a DT system and method which, in some embodiments, may result in reduced imaging times.